Extrusion blow molding (direct blow molding) is a process in which a thermoplastic resin is melted by an extrusion molding machine, the melted resin is discharged from an extrusion die (die head) to form a hollow tube-like parison, the parison is pinched between a pair of blow molding dies, and blow air is blown into the parison to form a hollow body.
Since a distal end of a parison in a state of being discharged from an extrusion die is not restricted in the state as it is, an axial shift and a thickness variation may occur due to a lateral vibration. In particular, a parison extruded vertically downward may have a thickness difference in the vertical direction due to a phenomenon that the parison itself is stretched by its own weight (draw-down) or a phenomenon that a diameter of the parison after being discharged from an extrusion die swells (die-swell).
In order to solve such a problem, a technique of pinching a parison discharged from an extrusion die using a chuck or the like has been proposed. Patent Literature 1 discloses a technique in which a parison is pinched by a pair of pinching units, a pinched parison section is cut and separated from a main parison, both pinching units are moved away from the main parison and are separated from each other to stretch the parison section in a vertical direction, and the parison section is inserted into a blow molding die in a state of being pinched by the pinching units.
Moreover, Patent Literature 2 discloses a technique in which a parison extruded from an extruding nozzle is captured by one capturing unit, the capturing unit is moved downward at a velocity greater than an extruding velocity of the parison to pull the parison, the parison in this pulled state is pulled into a molding die disposed below the extruding nozzle, and the parison is captured by another capturing unit disposed above the molding die before the parison section sandwiched by the molding die is separated from the main parison.